Rancho grande harlequin frog (Atelopus cruciger)

Also known as: Veragua stubfoot toad
Synonyms: Atelopus cruciger cruciger, Atelopus crucigerum, Atelopus varius cruciger, Phrynidium crucigerum, Phryniscus cruciger
  
Spanish: Sapito Rayado
KingdomAnimalia
PhylumChordata
ClassAmphibia
OrderAnura
FamilyBufonidae
GenusAtelopus (1)
SizeFemale snout-vent length: 24.6 - 28.2 mm (2)
Male snout-vent length: 33.4 - 39.5 mm (2)

The Rancho Grande harlequin frog is classified as Critically Endangered (CR) on the IUCN Red List (1).

The Rancho Grande harlequin frog (Atelopus cruciger) is a Critically Endangered amphibian which is endemic to the northern coastal mountains of Venezuela. Brought to the brink of extinction by the deadly fungal disease chytridiomycosis, this rare frog disappeared for almost 20 years until a small population was rediscovered in 2004 (1) (2). 

A beautifully marked species, the Rancho Grande harlequin frog has yellowish-green to olive-green upperparts, with black marbling or stippling. The underparts are yellow-cream, and there is a black or brown stripe running along the side of the body, from the snout to the vent. There is also a well-defined cross pattern behind the head, and the inner surfaces of the limbs are marked with dark brown or black (2) (3). 

The Rancho Grande harlequin frog is a relatively slender species, with a flat, triangular snout and long hind limbs and long feet. There is partial webbing on both the fore and hind feet, and the toes have swollen tips. Small, rounded warts run in a row down the back towards the vent, the outer surfaces of the limbs, and partly onto the hands. The male Rancho Grande harlequin frog has a broader, longer head than the female, as well as thicker fore limbs (2) (3).

Endemic to the northern coastal mountains of Venezuela, the Rancho Grande harlequin frog is known from several sites in the northern and southern regions of this mountain range. It is also known from Cerro Azul in the centre, which suggests that this species might be found throughout the central coastal range (1) (2).

The Rancho Grande harlequin frog is found in montane and lowland humid forests, where it breeds along swift-flowing streams. It occurs at elevations between 30 and 2,300 metres (1) (2).
 

Breeding typically occurs during the dry season so tadpoles are not washed away during heavy rain. During the breeding season, the Rancho Grande harlequin frog is usually found on rocks, around 1.5 metres above the ground, alongside fast-moving, cascading streams. Males spend much time alongside streams calling to females, using one of three distinct calls: pulsed ‘buzzes’, pure-toned ‘whistles’ that rise in frequency, or short ‘chirps’ and ‘twitters’ which decrease in frequency. When in the vicinity of other males, the male Rancho Grande harlequin frog may also emit a short, quiet, pulsed call. The female spends more time in the hillsides and in forests. Often the male finds the female away from the stream, and amplexus (the mating embrace) begins there. Amplexus may last for up to 19 days, before the female lays around 150 to 270 tan coloured eggs on substrate in a stream (2). 

The Rancho Grande harlequin frog is active during the day, when it feeds on ants and other insects. To dissuade predators, it secretes toxins from its skin which make it distasteful (2).

Frogs in the genus Atelopus have declined dramatically over recent decades, with 70 percent of the 113 known species thought to have suffered population crashes. In Venezuela, nine of the ten endemic Atelopus species are classified as Critically Endangered on the IUCN Red List, and one is thought to be extinct. The agent behind these declines is suspected to be chytridiomycosis, a disease caused by the pathogenic fungus Batrachochytrium dendrobatidis (4). 

Once abundant and widespread across the coastal mountains of Venezuela, the Rancho Grande harlequin frog has undergone a steep decline to the point that, despite extensive surveys, there were no observations of this species for almost 20 years after 1986 (5) (6). In 2004, after eight years of intensive searching, a small population of the Rancho Grande harlequin frog was discovered in the Parque Nacional Henri Pittier (2) (6). A number of other small populations have since been found (4). 

Analyses of specimens collected in 1986 confirmed that the Rancho Grande harlequin frog was suffering from infection by Batrachochytrium dendrobatidis (7). It is possible that an outbreak of chytridiomycosis occurred after severe droughts in 1988, which would have caused frogs to congregate at remaining water sources, increasing the speed of infection (2). Furthermore, over the last decade there has been a decrease in the maximum daily temperatures, which promotes the growth of Batrachochytrium dendrobatidis on amphibians. The fact that all surviving populations of the Rancho Grande harlequin frog occur below 350 metres above sea level, where temperatures are higher than at greater elevations, may be evidence of this (4). 

Other potential threats to the Rancho Grande harlequin frog include droughts and flash floods, which could increase in frequency as a result of climate change, and pollution in the Valencia-Maracay area, where many industries are emitting toxic gases (1) (2).

The habitat of the Rancho Grande harlequin frog is protected in a number of reserves, including Parque Nacional Henri Pittier, Parque Nacional Rancho Grande, and Parque Nacional San Esteban (1). It has also been recommended that this species be included in Appendix II of CITES, to ensure commercial trade across borders be maintained within sustainable levels (2) (5). 

Conservation recommendations for the Rancho Grande harlequin frog include monitoring its populations and assessing the prevalence of Batrachochytrium dendrobatidis, in case any new epidemics breakout. The development of ex-situ conservation measures is also urgently required for all Atelopus frogs, as long-term treatments to chytridiomycosis are difficult to apply in the field (4) (8).

Find out more about amphibian conservation:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

  1. IUCN Red List (May, 2011)
    http://www.iucnredlist.org/
  2. Amphibian Ark - Atelopus cruciger (May, 2011)
    http://amphibiaweb.org/cgi/amphib_query?where-genus=Atelopus&where-species=cruciger
  3. Lötters, S., La Marca, E. and Vences, M. (2004) Redescriptions of two toad species of the Genus Atelopus from coastal Venezuela. Copeia, 2004: 222-234.
  4. Rodríguez-Contreras, A., Celsa Señaris, J., Lampo, M. and Rivero, R. (2008) Rediscovery of Atelopus cruciger (Anura: Bufonidae): current status in the Cordillera de La Costa, Venezuela. Oryx, 42: 301-304.
  5. UNEP-WCMC (2008). Review of Non-CITES Amphibian species that are known or likely to be in international trade. Part II. A Report to the European Commission. UNEP-WCMC, Cambridge. Available at:
    http://ec.europa.eu/environment/cites/pdf/reports/amphibia_species_part2.pdf
  6. Atelopus.com - Atelopus cruciger (May, 2011)
    http://www.atelopus.com/index.php?option=com_content&view=article&id=86&Itemid=90
  7. Bonaccorso, E., Guayasamin, J.M., Méndez, D. and Speare, R. (2003) Chytridomycosis as a possible cause of population declines in Atelopus cruciger (Anura: Bufonidae). Herpetological Review, 34: 331-334.
  8. Lötters, S., Schulte, R., Córdova, J.H. and Veith, M. (2005) Conservation priorities for harlequin frogs (Atelopus spp.) of Peru. Oryx, 39: 343-346.